Is there an easy method to protect API keys? using Secrets.Json? etc?

I am signing the binary which should be encrypting it, but I would like to make sure my keys are not exposed. Hey everyone, I was curious if anyone has a way to implement a secret API key or Private key, etc using some protected method?
For instance,

var SecretKey = "Some key text or sequence";

I don't want a user to decompile the app and get that string.
I have seen in VS2019 there is a "Manage User Secrets" which opens a Secrets.Json file. How could I include a file that would compile / encrypt so as to protect the keys in it?

something like

{
    myAPP:
    {
        SecretKey : "Some key text or sequence",
    }
}

Has anyone use the Secrets.Json to implement secure keys in their app?

For the time being I am just using it for an API key, but in the future I may need to include an RSA key or something that would need to be secured.

Cheers!